Cardiolipin modulates the secondary structure of the presequence peptide of cytochrome oxidase subunit IV: a 2D 1H-NMR study.

The secondary structure of the presequence of cytochrome oxidase subunit IV (p25) was studied by circular dichroism and 2D nuclear magnetic resonance in micelles of dodecylphosphocholine (DPC) and mixed micelles of DPC and mitochondrial cardiolipin (CL). In both systems, alpha-helix formation was observed. The alpha-helix stretches from the N- to the C-terminus with a break at the proline residue at position 13. Upon introduction of CL in the DPC micellar system, an increased stability of the helix was observed around proline13 and in the C-terminal half. This observation, together with reported results on specific interactions between CL and p25, led to the proposal of a two-state equilibrium of the alpha-helical conformation of p25, modulated by CL.